New Free Mirai Scanner Tools Spot Infected, Vulnerable IoT Devices

Imperva is the latest security company to offer a free scanner to detect Internet of Things devices infected with or vulnerable to Mirai malware, the malicious code behind the massive distributed denial-of-service (DDoS) attacks on DNS provider Dyn.

The Mirai botnet army of IoT devices quickly gained notoriety earlier this year following major DDoS attacks on KrebsOnSecurity in September. The perpetrator released the Mira code publicly, and the malware was later used in the assault on Dyn, which led to the shutdown of prominent websites including Okta, CNN, Twitter, and Pinterest.

Mirai searches networks for Internet-connected consumer devices. It scans IP addresses across the Web to discover unsecured devices, and then guesses their login credentials. Once infected, the devices become part of the Mirai botnet that wages DDoS attacks. The Dyn attack, for example, used about 100,000 infected devices but still shut down prominent websites for much of the United States.

Rapid7 earlier this month released a scanner called IoTSeeker, which is designed to search users' networks and find common IoT devices with default usernames and passwords.

Mirai is also predatory, as explained in a blog post published by Imperva. Mirai can remove and replace malware previously installed on a device. Routers, IP cameras, and DVRs are especially vulnerable.

To mitigate the threat, security researchers are exploring new ways to detect vulnerable network devices before attackers can target them, with Imperva and Rapid7's scanning tools as one such method.

"The Mirai botnet scanner was developed to help home users, with IoT devices on their home network, learn if they are vulnerable to Mirai malware," says Robert Hamilton, director of product marketing manager at Imperva for its Incapsula product line.

Imperva's scanner checks whether one or more network devices is infected by, or vulnerable to, Mirai malware. When users instruct the tool to scan a network, it discovers the network's public IP address and checks the gateway from outside to see if any remote access ports are vulnerable to Mirai attack.

If the Mirai scanner finds a vulnerability, users will see a message indicating the IP address is hosting an IoT device vulnerable to Mirai injection attacks. In this case, Imperva recommends logging into each IoT device on the network and strengthening the password; however, it's worth noting that this step may not necessarily prevent attacks.

Hamilton noted Imperva's tool is also useful for the enterprise. Businesses can still be exposed to DDoS attacks from the Mirai botnet, whether or not they have IoT devices at risk.

"A business could use the tool to understand if they had any IoT devices on their network that might be vulnerable," Hamilton says. "However, the biggest risk to a business is that they become a target of the botnet by way of a DDoS attack. They don't need to have any vulnerable IoT devices to have that happen."

The scanner is designed so that it cannot be abused by bad actors, he says. "It will only test the IP address of the network the user is connected to," he says. "The tool cannot be used to probe other IP addresses or other remote networks."

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According to notes on the GitHub for Rapid7's IoTSeeker, the scanner is designed to search for specific types of IoT devices to see if they are using factory-set credentials.

"The recent Internet outage has been attributed to use [of] the IoT devices (CCTV Cameras, DVRs, and others) with default credentials," the notes state. "It's the intention of this tool to help organizations scan their networks to detect these types of IoT devices and to identify whether credentials have been changed."

IoTSeeker was built to scan thousands of IoTs at the same time, and only runs on Linux or MacOS.

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